I have had many opportunities to talk with amateur stargazers from all over the world, and I haven’t found a more dedicated lot than the ones who live in central Ohio.
We live under some of the cloudiest skies in North America. We must battle the behemoth glow of Columbus street lights. How is it that our dedication greater than those who live in, say, the nearly cloudless and lightless high desert of Arizona?
Given the difficulties, it’s a pleasure to report that many astronomical objects are visible through the central Ohio haze. Two of the best are the clusters of stars near the stinger of the constellation Scorpius, the Scorpion.
Scorpius is one of the few constellations that remain visible under even the worst light pollution. Right now, it sits close to the southern horizon just after dark at around 10 p.m. It even looks a bit like a scorpion, a tilted, elongated, capital-letter “J.” The Scorpion’s stinger curves to the far left. Up and to the left of the stinger are the clusters in question, M6 and M7.
You won’t see them with the unaided eye although the lower cluster, M7, is visible without optical aid from dark, rural skies.
In binoculars, M7 resolves easily into about 20 stars spread pretty much across the field of view. M6 looks like a little fuzzy patch just up and to the right from M7. You’ll need a telescope to resolve it into individual stars. If you can fit both clusters into the field of your binoculars, you’re in for a treat. The contrast between the resolved stars of M7 and the unresolved haze of M6 is quite lovely.
The difference in appearance is mostly a matter of the distance to the two clusters. Both contain about 80 stars, but M7 is much closer to us at a bit under 1,000 light years away. (One light year is about six trillion miles.) At 1,600 light years away, M6 appears much smaller and more difficult to resolve into individual stars. The clusters may look close together, but that illusion is created by our celestial vantage. They are actually separated along our line of sight by an unimaginable gulf – about 3,600 trillion miles.
Open clusters like M6 and M7 are made up mostly of brand-new, baby stars that recently formed together out of the same gigantic cloud of hydrogen. The stars in any given cluster are thus brothers and sisters formed from the same cosmic mother. If we measure their births against the vast age of the universe, they were all born at approximately the same time, just a few millions or tens of millions of years apart. Stars are born together in litters, like puppies.
However, the clouds are so large and the stars in them so far apart that their filial proximity is a temporary condition. The loose gravitational pull holding them in a cluster is insufficient to keep the family together. Over hundreds of millions of years, they will inevitably drift apart. The fact that they are still together at all suggests that M6 and M7 are relative newcomers to our galaxy, the Milky Way.
M6 is a scant 100 million years old. M7 is twice M6’s age, and that might sound ancient, but it isn’t. An average star like our sun hangs around the galaxy for 10 or 11 billion years before its thermonuclear fires are snuffed out. The stars of the clusters are, relatively speaking, stellar youngsters.
You can see then for yourselves, brave central Ohioans, but it won’t be easy. Arizonans can look at the stars any time they want. The stars are common as dirt to them. You must struggle a little to see the splendors of the universe. Just try to get a few hours sleep before you drive to work.
Stargazing at Perkins
The sun is finally setting a bit earlier, so our Fright-night public programs will shift to an 8 p.m. start time in September and throughout the rest of the year. Come on down for viewing with the big Schottland reflecting telescope if it’s clear. If it’s cloudy, we’ll teach you how observe the sky yourself with binoculars or our own two eyes. We’ll also provide a tour of historic Perkins Observatory. And there just might be a ghost story in it for you, as well.
Call 740-363-1257 for more information or to order tickets, or check us out at perkins.owu.edu.
Tom Burns is director of the Perkins Observatory in Delaware.